Clamps are circuits that are used to protect against electrostatic discharge (ESD) in electronic devices. Clamps are so named because they fix or “clamp” the positive or negative peak variations of a voltage signal to a defined value by shunting the ESD discharge current. The timing elements of transient clamps may be implemented by using resistors and capacitors (RC). Such clamps are referred to as RC clamps. RC clamps have a number of advantages over other types of clamps including process portability, ease of simulation with standard metal oxide semiconductor field effect transistor (MOSFET) models, faster response times and lower conduction offset voltages.
RC clamps may use two main electrostatic discharge models to determine their RC time constant values. The first model is the human body model (HBM), which sets a high RC time constant value for the RC clamp. The second model is the charged device model (CDM), which sets a RC time constant value that is lower than the one set by the human body model. The human body model may be used to calculate the RC time constant values of RC clamps. Unfortunately, the RC components for meeting these RC time constant values may take up nearly half of the entire layout area of the overall RC clamp.